Fatty acids (FA) are bioactive molecules which have potential as adjunctive chemotherapeutic agents. FA are classified as short-, medium; or long-chain on the basis of the number of carbon atoms in the aliphatic chain and have been reported to induce apoptosis in vitro in a range of cancer cell types, including breast, tongue, cervix and colorectal. However, to date the chain length exerting optimal anti-neoplastic properties remains undefined. Short chain fatty acids, such as butyrate (C4:0), have induced high rates of in vitro apoptosis, presumably related to epigenetic modification, cell cycle arrest and activation of pro-apoptotic genes. Medium chain fatty acids have demonstrated in vivo and in vitro cytotoxic and anti-microbial properties; however, scant evidence currently exists on their anti-neoplastic potential. Longer unsaturated fatty acids (C16-24: ω3-9), including conjugated linoleic acid and eicosapentaenoic acid, also exhibit in vitro anti-proliferative actions, including induction of oxidative stress and modification of intracellular signalling pathways. Although incorporation of FA into CRC chemotherapy regimens is in its infancy, evidence is accumulating to allow identification of the FA chain length capable of exerting the most effective anti-neoplastic activity.